Potassium

Question 1

Cellular functions of K+:

Answer 1

protein and glycogen synthesis

Question 2

Normal extracellular K+:

Answer 2

4-5 meq/L

Question 3

Electrical function of K+:

Answer 3

maintains resting membrane potential

Question 4

Sx of low or high K+:

Answer 4

cramps

muscle weakness/paralysis

EKG changes/arrhythmias

**relates to the inability of muscles to generate action potentials

Question 5

EKG changes in hyp-O-kalemia:

Answer 5

PR prolongation

ST depression

flattened or inverted T wave

U waves (right after T wave)

QRS widening

Question 6

EKG changes in hyp-ER-kalemia:

Answer 6

PR prolongation

ELEVATED T waves

widened QRS

Question 7

What increases threshhold potential and protects against the decreased resting potential of hyp-ER-kalemia?

Answer 7

hypercalcemia

Question 8

Releases K+ from cells in exchange for HCl buffering, exacerbating hyperkalemia?

Answer 8

metabolic acidosis

Question 9

Hypokalemia _______ digoxin toxicity but hyperkalemia ______ digoxin toxicity.

Answer 9

increases

causes

Question 10

Molecules that move K+ into cells:

Answer 10

insulin

catecholamines

Question 11

How do insulin and catecholamines get K+ into cells?

Answer 11

increased activity of Na-K-ATPase

increase uptake in skeletal muscle and liver

Question 12

Acidemia effect on serum K+:

Answer 12

Increases as H+ is buufered in to cells

Question 13

Alkalemia effect on serum K+:

Answer 13

Decrease as H+ is buffered into extracellular fluid

Question 14

If K+ lost in stool or sweat is clinically relevant?

Answer 14

Pathologic

Question 15

Major route of K+ elim?

Answer 15

Kidney

Question 16

Determinants of K+ secretion by kidney:

Answer 16

plasma concentration

urine flow in distal tubule

ALDOSTERONE: K+ secretion by PRINCIPAL cells of collecting tubule

Question 17

How does K+ get reabsorbed in loop of Henle?

Answer 17

NKCC pump

Question 18

How can K+ get reabsorbed during severe hypokalemia?

Answer 18

Intercalated cells in collecting tubule

alpha cells – K+/H+ antiporter

Question 19

Distal tubule secretion of K+ involves?

Answer 19

Principal cells

• luminal Na+ and K+ channels
• basolateral Na-K-ATPase

ALDOSTERONE

• very sensitive to K+ change (responds to 0.1 meq increase)
• increases Na and K channels
• increases activity of NA-K-ATPase

K conc gradient

distal flow is permissive??

Question 20

Causes of hyp-O-kalemia:

Answer 20

decreased intake (rare)

increased entry into cells (acidemia)

increased GI loss

increased urinary loss

increased sweat loss

dialysis

Question 21

Dietary phenomena that binds K+ leading to hypokalemia?

Answer 21

Clay ingestion

Question 22

Three causes of hypokalemia due to increased cellular uptake:

Answer 22

metabolic acidosis

hyperinsulinemia

increased catecholamines

Question 23

Causes of hypokalemia due to increased urinary loss?

Answer 23

Increased distal flow due to impaired salt and water reabsorption

• diuretics
• salt wasting nephropathies
• polydypsia/polyuria

Hypercalcemia

Mineral corticoid excess (Aldosterone)

Hypomagnesemia (effects K channels)

Question 24

How would you determine if K loss was due to kidney?

Answer 24

24 hour urine K+ test

if low –> not kidney problem

Question 25

If you have a low urinary K (GI loss) and acidemia, what part of GI tract is responsible?

Answer 25

Lower GI (laxatives, cancer)

Question 26

If low urinary K (GI loss) and alkalemia, what part of GI tract is responsible?

Answer 26

Upper (vomiting)

Question 27

If K loss is kidney related with acidemia, what are the possible problems?

Answer 27

ketoacidosis type I or II renal tubular acidosis

Question 28

If K loss is kidney related and alkalemia is present in a normotensive patient, what could the problem be?

Answer 28

vomiting diuretics (early) Bartter's syndrome (inherited)

Question 29

Hypertensive alkalosis due to kidney loss of K with high renin could be from:

Answer 29

diuretics renovascular disease reninoma Cushings

Question 30

Hypertensive alkalosis due to kidney loss of K with low renin could be from:

Answer 30

low aldosterone (or high???)

Question 31

Drugs that can cause hyperkalemia in the setting of normal total body K:

Answer 31

succinylcholine beta blockers digoxin

Question 32

Most common cause of hyperkalemia:

Answer 32

renal failure

Question 33

Major hormone responsible for renal excretion of K?

Answer 33

Aldosterone

Question 34

First thing to do to treat hyperkalemia?

Answer 34

Calcium IV

Question 35

Second things to do to get K into cells in Hyperkalemia?

Answer 35

Glucose and insulin NaHCO3 Beta-agonist (albuterol nebs) 3% NaCl if hyponatremic

Question 36

Long term(ish) treatment (hours) for hyperkalemia:

Answer 36

loop diuretics cation exchange (kayexalate) dialysis